This section is intended to introduce the reader to various aspects of the art that may be related to various aspects of the present invention. The following discussion is intended to provide information to facilitate a better understanding of the present invention. Accordingly, it should be understood that statements in the following discussion are to be read in this light, and not as admissions of prior art.
The current ultrasonic flow meter arrangement uses two transducers at opposing ends of a pipe where one is upstream from the fluid flow and other is downstream from the fluid flow, both transducers transmit and receive signals. Each transducer generates plane waves into the fluid and surrounding pipe wall. The difference in transit times between the upstream and downstream signal is used to calculate the flow rate. Since sound travels faster in the pipe wall than in the fluid medium, the receiving transducer has noise because the sound enters the pipe and arrives at a time preceding the sound that travels in the liquid. The noise level is significant because it reduces the accuracy of the flow measurement and results in a poor or no measurement at low flow rates.
Furthermore, traditionally, polymers with scattering fillers (such as metal or glass or microspheres) are used as backing masses for ultrasonic transducers. The use of an attenuative backing mass improves the bandwidth of the transmitted ultrasound signal of a transducer by absorbing the sound from the back side of the transducer and not allowing reflections to occur. Polymers with scattering fillers, it is believed, have never been used as pipe wall sound attenuators in the use of an ultrasonic transit time flow measurement.